1. Field of the Invention
This invention relates to hypodermic needles. More particularly, the invention relates to microneedles and fabrication methods thereof.
2. Description of the Related Art
Transdermal drug delivery represents a novel drug delivery route with little damage or pain. Such a drug delivery method has overcome the shortcomings in oral route that the drugs may be degraded in the gastrointestinal tract or be eliminated through the liver. Hence it has now been widely recognized as one of the most promising techniques with numerous commercial applications. The outer layer of skin (stratum corneum) is the most important barrier that prevents the drugs entering into the body. How to break through the stratum corneum painlessly and effectively is the key technique in transdermal drug delivery. Among the transdermal drug delivery techniques, hollow microneedle arrays have now been widely recognized as one of the most promising techniques. It can deliver drugs by painlessly piercing through the stratum corneum without reaching the dermis layer. Compared with methods of ion-implantation and electroporation, the holes throughout the stratum corneum generated by microneedles are much bigger and can delivery macromolecules, super-molecules, or even the particles into the body. Therefore, the fabrication methods for microneedles remain a hotspot research area in recent years. In the early stage, the fabricated microneedles are solid ones and can let the drugs diffuse into the body by generating holes in the skin. Recently, hollow microneedles are proposed for their advantages of the combination of microneedles and drug delivery. The drugs can be delivered into the skin through the tunnels existing in the hollow microneedles, which can greatly improve the efficiency of drug delivery and instantly control the drug species as well as their dosages painlessly and conveniently. However, the fabrications of hollow microneedle arrays mainly relied on the microfabrication techniques of a modified-LIGA process, a combination of deep reactive ion etching (RIE) and isotropic etching techniques, femtosecond laser two photon polymerization, deep x-ray lithography (DXRL) process, photo lithography, inductively coupled plasma (ICP) etcher, focused ion beam (FIB)-assisted technology, etc. In these cases, achieving commercial mass production of hollow microneedle arrays have been hindered greatly mainly by the inherent high cost and low throughput of the existing fabrication methods. Usually, the cost originated from microfabrication processes can be shared by many replicas to ensure the overall low cost. But this case was no longer effective for fabrication of hollow microneedle arrays using the current methods, because the mold had to be sacrificed during the fabrication processes and each mold can be used for only one time. Moreover, the hollow microneedles can be used for only one time to avoid cross infection and contamination. Up to now, it still remains a great challenge to fabricate hollow microneedle arrays efficiently and cost-effectively by commercially mass production, which greatly restricts their applications.